Among display apparatuses, a liquid crystal display apparatus is a thin type display and has characteristics such as low power consumption. A display panel of the liquid crystal display apparatus has a color filter (CF) substrate, a liquid crystal layer, an active matrix substrate (TFT substrate), and two polarizing plates. The CF substrate and the active matrix substrate are bonded to each other with a seal material interposed therebetween, and liquid crystal is arranged therebetween to form the liquid crystal layer. The active matrix substrate has pixel electrodes on the liquid crystal layer side, and the CF substrate has common electrodes on the liquid crystal layer side. The two polarizing plates are disposed on a surface opposite to the liquid crystal layer side of each of the CF substrate and the active matrix substrate.
The liquid crystal display apparatus using a vertical alignment type material as a liquid crystal material is called a vertical alignment (VA) mode liquid crystal display apparatus. The liquid crystal display apparatus, in order to improve transmittance and response speed thereof, has an alignment division structure in which a plurality of liquid crystal domains are formed in one pixel. As a method of forming the alignment division structure, there may be a multi-domain vertical alignment (MVA) mode. In the MVA mode, an alignment regulation structure is obtained by providing a linear projection on the liquid crystal layer side of the substrate which sandwiches the liquid crystal layer, and providing an opening part (slit) on the pixel electrode. By the alignment regulation structure, a plurality of liquid crystal domains are formed in the pixel (for example, Japanese Patent Laid-open Publication No. 2003-149647). By finely forming the slit, an alignment of the liquid crystal molecules may be more controlled, and the transmittance of light and response speed may be improved.
The VA mode, which is configured in such a manner that alignment films such as a photo alignment film are respectively provided on the liquid crystal layer sides of both substrates facing each other with the liquid crystal layer interposed therebetween so that pre-tilt directions (alignment treatment directions) are orthogonal to each other, and the liquid crystal molecules have a twist alignment during applying a voltage thereto, is called a vertical alignment twisted nematic (VATN) mode (for example, International Publication No. 2006/132369). Among them, a structure, in which four liquid crystal domains which are divided into two rows and two columns during applying a voltage thereto are formed in one pixel region, by defining the pre-tilt directions using the two alignment films, is called a 4D structure.
FIG. 36 is a plan view illustrating a pixel region of the VATN mode liquid crystal display apparatus having the 4D structure.
In FIG. 36, dotted line arrows illustrate pre-tilt directions which are defined by the photo alignment film provided on the active matrix substrate, and solid line arrows illustrate pre-tilt directions which are defined by the photo alignment film provided on the CF substrate. In addition, a tilt direction (standard alignment direction) of each liquid crystal domain when a voltage is applied to the liquid crystal layer is illustrated by a direction of pins. FIG. 36 illustrates that the liquid crystal molecules are tilted so that circular plate parts (head parts) of the pins are close to a viewer who views the liquid crystal display apparatus. That is, the standard alignment direction is oblique 45°. As described above, liquid crystal domains A, B, C and D are formed.
The pixel electrode of the liquid crystal display apparatus has no slit formed therein.
FIG. 37 is a plan view illustrating a light transmission state of the pixel region in FIG. 36. FIG. 37 illustrates a state in which a wiring and a contact hole are disposed. The contact hole is formed in a central part of the pixel region.
From FIG. 37, it can be seen that dark lines having a wide width are generated along a short side of the pixel region and a boundary between the liquid crystal domains. In the short side of the pixel region, the liquid crystal molecules are inclined in an orientation inward and perpendicular to the short side, and in the vicinity of the short side of the pixel region, the head parts of the liquid crystal molecules inclined on the short side and the liquid crystal molecule aligned in the tilt direction face each other, as well as the direction of the liquid crystal molecules is disturbed, and the liquid crystal molecules are bent in a direction perpendicular or parallel to the polarizing axes, such that a region through which the light is not transmitted occurs. In the boundary between the liquid crystal domains, tilt angles on both sides of the boundary are 90° different from each other. Therefore, the liquid crystal molecules are aligned with being bent in a direction perpendicular to the boundary (a direction perpendicular or parallel to polarizing axes), and thereby a wide region through which the light is not transmitted occurs.
The transmittance of light is decreased by the dark lines. Particularly, in a high definition display having small pixels, the effect of a decrease in transmittance of light by the dark lines becomes larger.
Assembling the above-described MVA mode in the VATN mode having a 4D structure has also been attempted (for example, International Publication No. 2013/054828 and the like).
FIG. 38 is a plan view illustrating a pixel electrode of the active matrix substrate in the pixel region of a liquid crystal display apparatus of International Publication No. 2013/054828.
Four liquid crystal domains of the pixel electrode respectively have a group of slits 21 which extend in each tilt direction of oblique 45° formed therein. By the slits 21, the above-described dark lines generated at the boundary portion between the liquid crystal domains of the VATN mode are reduced, and thus the transmittance of light may be increased. A contact hole 12 is formed in the central part of the pixel region.
FIG. 39 is a plan view illustrating the light transmission state of the pixel region in FIG. 38. FIG. 39 illustrates a state in which the wiring and the contact hole are disposed.
Also in this structure, it can be seen that dark lines having a constant width are formed at the boundary portion, and a sufficient effect may not be obtained. In addition, the dark lines along the slits 21 also occur.